1. Technical Field
The present invention relates to an imaging apparatus that uses an imaging device to detect light focused by various types of lenses, such as a fisheye lens and a wide-angle lens, enlarges some of image signals detected by the imaging device, corrects distortion, and displays an image on a display screen.
2. Related Art
An imaging apparatus that uses a camera including a fisheye lens or an optical lens and an imaging device to capture an external image and displays the image on a display device has been used for security or vehicles. In particular, in an imaging apparatus for a vehicle, a camera is attached to the body of the vehicle and captures an external image in the wide range. However, the distortion of an image detected by an imaging device of a camera using a fisheye lens or a wide-angle lens is increased as a field angle from the optical axis of the lens is increased.
Therefore, JP-A-2000-324386 discloses a technique that calculates the distortion of an image captured by a camera and corrects the distortion of the image. However, JP-A-2000-324386 does not disclose a method of calculating the distortion. Since the image captured by the camera using the fisheye lens or the wide-angle lens has a three-dimensional depth, a three-dimensional geometric process is needed to calculate the distortion of the image, which results in an increase in the amount of computation. In addition, a large load is applied to a CPU in order to continuously calculate the distortion of the image captured by the camera using the fisheye lens or the wide-angle lens.
JP-A-2004-40411 discloses a display system which includes a conversion table that corrects the distortion of a curved image and uses the conversion table to convert the curved image captured by a camera into display data.
However, in this method, the conversion table corresponds to only a section having a predetermined size that is disposed at a predetermined position of the image captured by the camera. Therefore, when a plurality of sections is extracted from the image captured by the camera and then displayed on a display device, it is necessary to prepare the conversion table for each of the sections. That is, since the conversion table corresponds to a predetermined region of the image captured by the camera, the conversion table has low compatibility. For example, when the angle at which the camera is attached deviates from the original position and the actual image is different from the image of a predetermined section in the conversion table, it is difficult to exactly correct the captured image.
Japanese Patent No. 3300334 discloses a technique in which a matching table corresponding to a display region is prepared in advance, and pixels of images captured by a plurality of cameras are displayed to correspond to predetermined coordinates in the matching table. Similar to the disclosure of JP-A-2004-40411, the arrangement disclosed in Japanese Patent No. 3300334 can correct only the distortion of an image in a predetermined section.
In addition, since the corrected image is subjected to plane development, the overall field angle of the image is decreased.